1. Field of the Invention
This invention relates to a process for preparation of organosilver carboxylates, in particular, to a process for preparation of fine particles of organosilver carboxylates which can advantageously be used in the manufacture of heat developable photographic materials.
2. Description of the Prior Art
Use of organosilver carboxylates as heat developable photographic materials has already been described, for example, in U.S. Pat. Nos. 3,589,901, 3,152,904, 3,457,075, and 3,589,903. These heat developable photographic materials essentially consist of an organosilver carboxylate such as silver behenate, a silver halide formed by the reaction of the silver salt with a halide or a silver halide separately formed and added, and a reducing agent.
After these heat developable photographic materials are exposed imagewise and then heated, silver images are formed due to the reaction of organosilver carboxylate and reducing agent caused by the catalytic action of the sensitized silver halide and the subsequent heating to follow.
A method for preparation of organosilver carboxylates which are suitable for manufacture of heat developable photographic materials is described for example in U.S. Pat. No. 3,458,544, where a solution of an organic carboxylic acid dissolved in a solvent which is difficultly soluble in water is admixed with an alkali-soluble silver complex aqueous solution to form fine organo silver carboxylate particles.
Organosilver carboxylates prepared by this method must necessarily be washed with water for the purpose of removing the alkali content contained in the silver complex aqueous solution. This is because, when organosilver carboxylates which have not been washed with water are used for manufacture of heat developable photographic materials, good images cannot be produced due to occurrence of strong fog in heat development.
However, even though the washing with water is carried out, the alkali content cannot completely be removed, and so it is impossible to completely prevent the occurrence of fog in heat development. Therefore, the use of an anti-fogging agent such as mercury compound has been inevitable, in order to obtain good image free from any fog. However, mercury compounds are toxic and so the use thereof is not desired.
In addition, the silver salts prepared by the method as described in U.S. Pat. No. 3,458,544 are further defective in that, when applied to a film, the materials are cloudy white. This is a fatal defect in manufacture of films for producing images which are to be observed using transmitted light.